JP2001168767A - Spread spectrum signal demodulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spread spectrum signal demodulator where noise components included in respective demodulated symbols are reduced and the effect of interference elimination is increased. SOLUTION: Symbol correlation detection means 111-11K detect the correlation of spread codes allocated to spread spectrum signals to be removed and reception signals. A symbol judgment means 121 synthesizes one or plural 1- symbol correlation values b1-bk in a common mode, that is performs diversity synthesis, and performs symbol judgment. For the symbol judgment, hard judgment or soft judgment can be used. Correlation value correction means 131-13K input the 1-symbol correlation values b1-bk outputted from the symbol correlation detection means 111-11K and a symbol judged result outputted by the symbol judgment means 12 and correct the symbol correlation values b1-bk. The corrected symbol correlation values d1-dk are sent to interference signal duplication means 141-14K and spectrum spread by the pertinent spread code.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum signal demodulation apparatus, and more particularly to a spread spectrum signal demodulation apparatus used in a cellular communication system, a private wireless communication system, a wireless LAN system, etc., and having improved interference removal capability. About.

[0002]

2. Description of the Related Art In a communication using a spread spectrum signal, a modulation symbol to be transmitted is further modulated by a high-speed spreading code (this is called secondary modulation) to obtain a signal having a spectrum width larger than the information bandwidth. Transmit information. On the receiving side, the received signal is despread to extract modulation symbols. Here, despreading is a process of performing convolution integration of a received signal with a conjugate complex number of a spreading code assigned to one modulation symbol. The symbol correlation value obtained as a result is a demodulated symbol, and in the related art, the correlation value for one symbol is directly used as a demodulated symbol for transmission information extraction.

[0003] In some cases, the modulation symbol is modulated as it is as the transmission information, or it is modulated after the transmission information is coded for error correction. As a receiving method, there is a method of directly extracting transmission information from a demodulated symbol, or a method of duplicating an interference component from a demodulated symbol of an interfering station, subtracting this from a received signal, and then extracting target transmission information.

An example of the latter receiving method, that is, a receiving method based on interference cancellation, which can be applied regardless of the presence or absence of pilot symbols, will be described with reference to FIG. The received signal 1 is input to the symbol correlation detecting means 11 and the subtractor 13. The symbol correlation detecting means 11 obtains a correlation value for one symbol and outputs it to the interference signal duplicating means 12. The interference signal duplicating means 12 creates duplicates of the individual spread spectrum signals included in the received signal by re-spreading the input correlation value with a spreading code in accordance with the timing of each transmission symbol. The subtractor 13
The duplicate signal is removed from the received signal 1, and the symbol correlation detecting means 14 calculates a correlation value between the received signal after the duplicate signal removal and the spread code assigned to each spread spectrum signal included in the received signal. The information demodulating means 15 demodulates the correlation value and outputs the result as demodulated information.

Next, a method applicable only to a transmission system having pilot symbols will be described with reference to FIG.
Note that the same reference numerals as those in FIG. 10 have the same or equivalent functions, and a description thereof will not be repeated. Transmission path estimation means 16
Estimates the transmission path condition from the pilot symbols detected by the symbol correlation detecting means 11 and
7 temporarily determines a symbol from the correlation value for one symbol.
The interference signal duplicating means 12 multiplies the tentative determination result by the transmission path estimation value, and uses the result as a duplicate of the interference component.

[0006]

In each of the above-described reception methods using interference cancellation, since each demodulated symbol is determined from the correlation value for one symbol, the noise included in the correlation value for one symbol is used. There is a problem that the components degrade the quality of the duplicated interference signal and reduce the accuracy of interference removal.

The present invention eliminates the above-mentioned problems of the prior art, reduces noise components included in individual demodulated symbols,
It is an object of the present invention to provide a spread spectrum signal demodulation device in which the effect of removing interference is increased.

[0008]

In order to achieve the above object, the present invention provides a spread spectrum signal demodulation apparatus which receives a spread spectrum signal as an input. Symbol correlation detection means for detecting a correlation value, symbol determination means for determining a transmission symbol based on the symbol correlation value detected by the symbol correlation detection means, and symbol determination result based on the symbol determination result determined by the symbol determination means A first feature is that a correlation value correcting means for correcting a symbol correlation value is provided to reduce a noise component included in each demodulated symbol.

Further, the present invention provides a symbol correlation detecting means for detecting a symbol correlation value between a spread code assigned to a spread spectrum signal and a received signal, and a symbol correlation value detected by the symbol correlation detecting means. A symbol determination unit with reliability that determines the transmission symbol and outputs the reliability of the symbol determination result, and a correlation value correction that corrects a symbol correlation value based on the symbol determination result determined by the symbol determination unit with reliability. There is a second feature in that a noise component included in each demodulated symbol is reduced.

According to the first and second aspects of the present invention, pilot symbol free (known information for estimating a channel state such as a pilot symbol is transmitted, which is a feature of a duplicated signal elimination method based on a conventional soft decision criterion, is transmitted. (A method that can be applied even to a method that is not performed) can be maintained, and the interference removal ability can be improved. Further, even when the pilot symbol is applied to a certain transmission scheme, the interference removal ability can be similarly improved.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a spread spectrum signal demodulator according to one embodiment of the present invention.
This embodiment can be applied not only to a transmission scheme with pilot symbols but also to a transmission scheme without pilot symbols.

The symbol correlation detecting means 111 to 11K are:
It detects the correlation between the spread code assigned to the spread spectrum signal to be removed and the received signal, and is realized by a correlator, a matched filter, or the like.

FIG. 2 is a block diagram of a specific example in which the symbol correlation detecting means 111 is configured using a matched filter. Note that the symbol correlation detecting means 112 to 11K have the same configuration as the symbol correlation detecting means 111, and thus the description is omitted. The matched filter 21 obtains an instantaneous correlation value a between the received signal 1 and the spreading code. The path detector 22 detects the presence of the target signal from the result. Finger catcher 2
3 is detected path information (a kind of timing information)
, And captures the instantaneous correlation value a as a one-symbol correlation value b1.

The symbol determination means 121 performs symbol determination by combining one or a plurality of one-symbol correlation values b1 to bk in phase, that is, by performing diversity combining. As the symbol determination, a hard decision that outputs only a code or a symbol determination with reliability that outputs the reliability of the symbol determination result, for example, a soft decision that outputs a code and a combined signal strength can be used. In addition, the symbol determination with reliability outputs a large value to a determination result that is more certain, and outputs a small value to a determination result that is less certain, that is, weights the certainty of the determination result to make a determination. Things. When there is a reflector or the like in the transmission path or when there are a plurality of reception systems, the same transmission signal is received through a plurality of paths. Therefore, in-phase synthesis of a plurality of 1-symbol correlation values b1 to bk cannot be performed. It is significant.

FIG. 3 shows a specific example of the symbol determination means 121.
Shown in For each one-symbol correlation value b1 to bk, the symbol correlation value immediately before these is used as the symbol delay 3
1 to 3K, and their conjugate complex values are output from the conjugate calculators 41 to 4K. The multipliers 51 to 5K are:
The one-symbol correlation values b1 to bk and the conjugate operators 41 to 4
The output is multiplied by the output of K. As a result, the phase rotation received on the transmission path is removed, and the K one-symbol correlation values can be in-phase synthesized in the synthesizer 32. The symbol determiner 33 determines a demodulated symbol from the combined one-symbol correlation value.

The correlation value correction means 131 to 13K are means newly proposed by the present invention, and output by the symbol determination means 121 and the symbol correlation values b1 to bk output from the symbol correlation detection means 111 to 11K. The symbol correlation values b1 to bk are corrected using the symbol determination result as input.

FIG. 4 shows a specific example of the correlation value correcting means 131 for correcting the correlation value based on the correlation values of three consecutive symbols. The other correlation value correction units 132 to 13K have the same configuration. The input one-symbol correlation value b1 is 2
Two symbol delay units 61 and 62 store up to two symbols before. The symbol determination result c is stored up to two symbols before by the two-symbol delay unit 63. The conjugate value of the current symbol determination result c is calculated by the conjugate calculator 64, and the current one-symbol correlation value b1 and the multiplier 6 are calculated.
Multiplied by 5. On the other hand, for the input two symbols earlier, the multiplier 66 multiplies the symbol decision result c ′ two symbols earlier and the one symbol correlation value b1 ′ two symbols earlier.
The result of the multiplication and the correlation value of one symbol before one symbol are added by an adder 67. The added value (total value) is divided by "3" in a divider 68, and the symbol correlation value d1 obtained by correcting the result is obtained. And

The blocks after the correlation value correcting means 131 to 13K in FIG. 1 are the same as those used in the prior art. That is, the interference signal duplicating means 141 to 14K
The symbol correlation values d1 to dk of the interference signal are spread with the corresponding spreading codes, and if necessary, the spread spectrum signal is subjected to waveform shaping and signal strength suppression, and output as copies e1 to ek of the interference signal. I do.

FIG. 5 shows a specific example of the interference signal duplicating means 141. The other interference signal duplicators 142 to 14K have the same configuration. The inputted symbol correlation value d1 is multiplied by a suppression coefficient (usually 1 or less) by a multiplier 71, and its intensity is weakened. Next, after being re-spread with a predetermined spreading code by a re-spreader 72, a signal waveform whose band of the spread signal is limited by a waveform shaper 73 is output as a copy e1 of the interference signal.

The subtraction signal 151 subtracts the duplications e1 to ek output from the interference signal duplication means 141 to 14K from the reception signal 1, and outputs the result as a reception signal after interference removal. The symbol correlation detecting means 161 detects a correlation between a spread code assigned to a spread spectrum signal to be demodulated and a received signal after interference removal. The information demodulating means 171
This is for restoring transmission information based on a target demodulated symbol. If the transmission method has not been subjected to error correction coding or the like, the same operation as the symbol determination means 121 is performed. On the other hand, if error correction coding is applied,
A decoding operation corresponding to those encoding methods is performed.

Next, the effects of this embodiment will be described using mathematical expressions. Noise component included the channel state of the spectrum spread signal to remove a, the transmission symbols d _t corresponding to the time _t, the correlation value for one symbol corresponding to the time of outputting the symbol correlation detecting unit 111 s _t, a s _t To n _t
Then, the output of the symbol correlation detecting means 111 is
It is expressed by equation (1). _{s t = a · d t +} n t ... (1) It should be noted that all of the symbol is a complex number. It is assumed that | d _t | = 1 for simplicity of explanation.

The time output by the symbol determination means 121
Δ 差動 d is the differential symbol determination result corresponding to_tToss
You. If the result of this determination is correct, the relationship of equation (2) is satisfied.
You. Where x^*Is the complex conjugate of x. Δ ＾ d_t= D_t・ D^* _t-1 .. (2) repair corresponding to time t, output by the correlation value correcting means 131;
Positive correlation value ＾ s_tIs given by the following equation (3) from FIG. ＾ s_t= 1/3 (s_t-1・ Δ ＾ d_t+ S_t+
s_{t + 1}・ Δ ＾ d^* _{t + 1}… (3) Equation (1) and
By substituting equation (2) into equation (3), the following equation (4) is obtained.

[0023] _{^ s t = 1/3 (} s t-1 · Δ ^ d t + s t + s t + 1 · Δ ^ d * _{t + 1) = 1/3} [(ad t-1 + n t-1) d t · d * t-1 + (ad t + n t) + (ad t + 1 + n t + 1) d * t + 1 · d t] = a · d _{t +1/3 (n 't-1} + n t + n' t + 1) ... (4) _{here, n 't-1 = n} t-1 · d t · d *
_t-1 , n't _{+ 1} = _{nt +} 1.d ^* _{t + 1.
dt} . Since | d _t | = 1, the variance of n ′ is the same as the variance of n.

Therefore, the target signal power contained in the demodulated symbol output from the correlation value correcting means 131 is a ² , and the noise power is 3N / 3 ² = N / 3, where N is the variance of n. On the other hand, from the above equation (1), the one-symbol correlation detecting means 1
Target signal power 11 is contained in the demodulated symbol output noise power of what is a ² is N. That is, as an effect of the present embodiment, the noise power included in the demodulated symbol can be reduced to 1/3.

If there is an error in the symbol decision result Δ ＾ _dt output from the symbol decision means 121, the noise power is larger than １ ／, but the symbol decision error rate is at a practical level (about 10%). In the following case, an improvement effect can be obtained.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 6 is a block diagram showing the configuration of the present embodiment. This embodiment is applicable to a transmission scheme having pilot symbols.

The symbol correlation detecting means 211 to 21K are:
Since the configuration is the same as or equivalent to that of the symbol correlation detection means 111 to 11K of the first embodiment, the description is omitted.

The transmission path estimating means 231 to 23K extract pilot symbols from the demodulated symbols, and compare the extracted pilot symbols with pilot symbol patterns that should be transmitted. Is estimated.

The symbol determination means 221 combines one or a plurality of one-symbol correlation values f1 to fk in phase based on the transmission path conditions, that is, performs diversity combining,
The symbol is determined. The symbol determination can be a hard decision that outputs only the code, or a symbol determination with reliability that outputs the reliability of the symbol determination result, for example, a soft decision that outputs the code and the combined signal strength. When there are reflectors or the like in the transmission path or when there are a plurality of reception systems, the same transmission signal is received through a plurality of paths. Therefore, usually, a plurality of one-symbol correlation values are in-phase combined.

One specific example of the symbol determination means 221 is shown in FIG.
Shown in The symbol determination means 221 receives the respective one-symbol correlation values f1 to fk and the corresponding channel estimation values g1 to gk. The transmission path estimated values g1 to gk are converted into complex conjugate numbers through conjugate arithmetic units 81 to 8K, and then are multiplied by one of symbol multipliers 91 to 9K.
Multiplied by k, the phase rotation experienced by the transmission path is removed. As a result, in the combiner 101, a plurality of one-symbol correlation values f1 to fk can be combined in phase. The symbol determiner 102 determines a demodulated symbol from the combined one-symbol correlation value, and outputs a symbol determination result h.

The correlation value correcting means 241 to 24K are newly proposed means according to the present invention, and include one symbol correlation values f1 to fk output from the symbol correlation detecting means 211 to 21K and output from the symbol determining means 221. And the symbol correlation values f1 to f
Modify k.

FIG. 8 shows a specific example of the correlation value correcting means 241. Note that the other correlation value correction means 242 to 24K also
Same or equivalent configuration. A conjugate complex number is obtained from the input symbol determination result h by the conjugate calculator 103, and the one-symbol correlation value f 1 input by the multiplier 104 is obtained.
Is multiplied by The average value calculator 105 performs a process of obtaining an average value over a plurality of symbols on the multiplication result. On the other hand, the delay unit 106 stores the symbol determination result h for the time required for the processing of the average value calculator 105.
The multiplier 107 multiplies the result obtained by averaging the product of the symbol correlation value f1 and the conjugate complex number of the symbol determination result h by the average calculator 105 and the stored value of the symbol determination result h, and outputs the result.

The configuration after the correlation value correcting means 241 to 24K, that is, the interference signal duplicating means 251 to 25K, the subtractor 261, the symbol correlation detecting means 271, and the information demodulating means 281 are the same as those of the first embodiment. The description is omitted because they are the same or equivalent. It should be noted that the interference signal duplicating means 251 to 25K of the present embodiment has the symbol correlation value i output from the correlation value correcting means 241 to 24K.
1 to ik are input, but the conventional interference signal duplicating means 12 shown in FIG. 11 does not receive a symbol correlation value, and the transmission path estimation value (output of the transmission path estimation means 17) and the symbol determination result (symbol (The output of the determination means 17). Therefore, the interference signal duplication unit 2 of the present embodiment
51 to 25K and the conventional interference signal duplicating means 12 are different. Next, effects of the second embodiment will be described using mathematical expressions. The symbols used here have the same meaning as those used in the first embodiment.

The symbol determination result output from the symbol determination means 221 corresponding to time t is set to ＾ _dt . If the result of this determination is correct, the relationship of the following equation (5) is obtained. ＾ d _t = d _t (5) The average value obtained by the average value calculator 105 (see FIG. 8) of the correlation value correcting means 241 is represented by S. As an example, assuming that an averaged section is continuous m symbol times (m is a positive integer), S is given by equation (6) in FIG.

Next, the output i1 of the correlation value correcting means 241
(= ＾ s _t ) is expressed by the following equation (7). ＾ s _t = S · ＾ d _t (where j + 1 ≦ t ≦ j + m) (7) Next, when equation (1) is substituted into equation (6), equation (8) in FIG. 9 is obtained. By substituting equations (5) and (8) into equation (7),
Equation (9) is obtained.

[0036] Thus, the target signal power included in the modified correlation value ^ _{s t} as ^{a 2,} the noise power variance of the n N, the ^{mN / m 2 = N / m} . That is, as an effect of the second embodiment of the present invention, noise power included in a demodulated symbol can be reduced to 1 / m times.

If there is an error in the symbol judgment result ＾ _dt output from the symbol judgment means 221, the noise power is larger than 1 / m times, but the symbol judgment error rate is at a practical level (about 10% or less). ), An improvement effect can be obtained.

As an example, d_tWith the BPSK signal
And when the bit error rate is 8%, the received symbol power
And the thermal noise power included in the symbol correlation value is equal
(A² = N), 0.3 dB (0.92
X), m = 4, 0.9 dB (0.82 times), m = 8
Improvement of about 1.4 dB (0.73 times) (reduction of noise power)
Small). Moreover, the average section symbol length m is free.
Can be set to improve the characteristics as needed
It is possible to

On the other hand, in the conventional spread spectrum signal demodulator shown in FIG. 11, even if there is no symbol decision error, the accuracy of the duplicated interference signal is substantially determined by the received power included in the pilot. It is difficult to improve quality. If there is an error in symbol determination,
Since the symbol determination result is directly re-spread, the accuracy degradation of the duplicated interference signal is greater than in the second embodiment.

As described above, according to the present invention, it is possible to accurately remove interference by correcting the symbol correlation value of an interference signal.

The first and second embodiments are merely examples, and are independent of the order of addition, subtraction, multiplication, and division, and the method of selecting an average correlation value section. The present invention includes anything that modifies one or more symbol correlation values.

The relationship between the signal-to-noise power ratio (SNR) of the symbol correlation value and the SNR of the corrected symbol correlation value is the same as the relationship between the SNR shown in the above formula (1), (4) or (9). What is the same is equivalent to the above embodiment.

The symbol determination usually means that a possible value of a transmission symbol is determined before final determination. However, even if the possible value of the symbol determination result is other than the possible value of the transmission symbol, the same effect as in the present embodiment can be obtained. As an example, the same effect as in the embodiment shown here can be obtained even in a case where a certain amount of offset is given to a value that can be taken by a transmission symbol. Alternatively, even if the total number of possible values of the symbol determination result is different from the total number of possible values of the transmission symbol, the same effect as in the present embodiment may be obtained depending on how to select the possible values.

That is, the main part of the present invention is that a complex weighted average (including real number weighting) is used for a plurality of symbol correlation values at different times.
Is included, and the symbol correlation value is corrected, and it is not possible to deviate from the scope of the present invention by changing the averaging method and the symbol determination method.

[0045]

As described above, according to the present invention, the symbol correlation value is corrected based on the determination result of the received symbol determined by the symbol determination means, so that an interference signal having a small noise level can be reduced. Be able to duplicate. Also, for this reason, the interference removal capability can be improved by subtracting the thus-obtained duplicated signal with a small noise level from the received signal or the received signal from which some interference components have already been removed. Become like Further, the present invention can be flexibly applied to a transmission system that does not use pilot symbols.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a first exemplary embodiment of the present invention.

FIG. 2 is a block diagram illustrating a specific example of a symbol correlation detection unit according to the present embodiment.

FIG. 3 is a block diagram illustrating a specific example of a symbol determination unit according to the present embodiment.

FIG. 4 is a block diagram illustrating a specific example of a correlation value correcting unit according to the present embodiment.

FIG. 5 is a block diagram illustrating a specific example of an interference signal duplication unit according to the present embodiment.

FIG. 6 is a block diagram showing a configuration of a second embodiment of the present invention.

FIG. 7 is a block diagram illustrating a specific example of a symbol determination unit according to the present embodiment.

FIG. 8 is a block diagram illustrating a specific example of a correlation value correcting unit according to the present embodiment.

FIG. 9 is an explanatory diagram of a mathematical expression.

FIG. 10 is a block diagram illustrating an example of a conventional device.

FIG. 11 is a block diagram showing another example of the conventional device.

[Explanation of symbols]

111-11K, 211-21K ... symbol correlation detecting means, 121, 221 ... symbol determining means, 131-13
K, 241 to 24K... Correlation value correcting means, 141 to 14
K, 251 to 25K: interference signal duplicating means, 151, 26
1 ... subtracter, 161, 271 ... symbol correlation detection means,
171, 281... Information demodulation means.

Claims (7)

[Claims] 1. A spread-spectrum signal demodulation apparatus which receives a spread-spectrum signal as input, comprising: a symbol-correlation detecting means for detecting a symbol correlation value between a spread code assigned to the spread-spectrum signal and a received signal; A symbol determining unit that determines a transmission symbol based on the symbol correlation value detected in step (a), and a correlation value correcting unit that corrects the symbol correlation value based on the symbol determination result determined by the symbol determining unit. A spread spectrum signal demodulation apparatus characterized in that a noise component included in a demodulated symbol is reduced. 2. A spread spectrum signal demodulation apparatus to which a spread spectrum signal is input, wherein: a symbol correlation detection means for detecting a symbol correlation value between a spread code assigned to the spread spectrum signal and a received signal; Determining a transmission symbol based on the symbol correlation value detected in step (a) and outputting a reliability of the symbol determination result; and a symbol determination result based on the symbol determination result determined by the reliability-determined symbol determination unit. A spread-spectrum signal demodulation apparatus, comprising: a correlation-value correcting unit that corrects a symbol correlation value by reducing a noise component included in each demodulated symbol. 3. The spread spectrum signal demodulation apparatus according to claim 1, wherein said symbol decision means uses the hard decision data obtained by diversity combining the input symbol correlation values as a symbol decision result. 4. The reliability-determined symbol determining unit sets soft-decision data obtained by diversity-combining the input symbol correlation values as a reliability-determined symbol determination result. Spread spectrum signal demodulator. 5. A transmission path estimating means for estimating a state of a transmission path and outputting a transmission path estimation value, wherein the symbol judgment means or the reliability-determined symbol judgment means comprises the symbol correlation value and the transmission path 3. The spread spectrum signal demodulation apparatus according to claim 1, wherein a transmission symbol is determined based on the estimated value. 6. A first symbol delayer for delaying a one-symbol correlation value by n symbols (n is an integer of 2 or more), a second symbol for delaying the symbol determination result by n symbols, A delay unit; first multiplication means for obtaining a product of the one symbol correlation value and a conjugate complex number of the symbol determination result; one symbol correlation value delayed by the first symbol delay unit and the second symbol delay Multiplying means for obtaining a product of the symbol judgment results delayed by the delay unit, each output of the first and second multiplying means, and m symbols (m is an integer smaller than n) in the first symbol delay unit. )
3. The spread spectrum signal demodulation device according to claim 1, further comprising means for calculating an average value of the delayed one-symbol correlation values. 7. The conjugate calculating means for obtaining a conjugate complex number of the symbol determination result, the first multiplication means for multiplying the conjugate complex number obtained by the conjugate calculating means by one symbol correlation value, Averaging means for averaging the multiplication result of the first multiplication means over symbols larger than 1, delay means for delaying a symbol determination result, and second multiplication means for multiplying the outputs of the averaging means and the delay means. 6. The method according to claim 1, further comprising:
2. The spread spectrum signal demodulation device according to 1.